#ifndef  _MAVLINK_CONVERSIONS_H_
#define  _MAVLINK_CONVERSIONS_H_

/* enable math defines on Windows */
#ifdef _MSC_VER
	#ifndef _USE_MATH_DEFINES
		#define _USE_MATH_DEFINES
	#endif
#endif
#include <math.h>

#ifndef M_PI_2
	#define M_PI_2 ((float)asin(1))
#endif

/**
 * @file mavlink_conversions.h
 *
 * These conversion functions follow the NASA rotation standards definition file
 * available online.
 *
 * Their intent is to lower the barrier for MAVLink adopters to use gimbal-lock free
 * (both rotation matrices, sometimes called DCM, and quaternions are gimbal-lock free)
 * rotation representations. Euler angles (roll, pitch, yaw) will be phased out of the
 * protocol as widely as possible.
 *
 * @author James Goppert
 * @author Thomas Gubler <thomasgubler@gmail.com>
 */


/**
 * Converts a quaternion to a rotation matrix
 *
 * @param quaternion a [w, x, y, z] ordered quaternion (null-rotation being 1 0 0 0)
 * @param dcm a 3x3 rotation matrix
 */
MAVLINK_HELPER void mavlink_quaternion_to_dcm(const float quaternion[4], float dcm[3][3])
{
	double a = quaternion[0];
	double b = quaternion[1];
	double c = quaternion[2];
	double d = quaternion[3];
	double aSq = a * a;
	double bSq = b * b;
	double cSq = c * c;
	double dSq = d * d;
	dcm[0][0] = aSq + bSq - cSq - dSq;
	dcm[0][1] = 2 * (b * c - a * d);
	dcm[0][2] = 2 * (a * c + b * d);
	dcm[1][0] = 2 * (b * c + a * d);
	dcm[1][1] = aSq - bSq + cSq - dSq;
	dcm[1][2] = 2 * (c * d - a * b);
	dcm[2][0] = 2 * (b * d - a * c);
	dcm[2][1] = 2 * (a * b + c * d);
	dcm[2][2] = aSq - bSq - cSq + dSq;
}


/**
 * Converts a rotation matrix to euler angles
 *
 * @param dcm a 3x3 rotation matrix
 * @param roll the roll angle in radians
 * @param pitch the pitch angle in radians
 * @param yaw the yaw angle in radians
 */
MAVLINK_HELPER void mavlink_dcm_to_euler(const float dcm[3][3], float* roll, float* pitch, float* yaw)
{
	float phi, theta, psi;
	theta = asin(-dcm[2][0]);

	if(fabsf(theta - (float)M_PI_2) < 1.0e-3f) {
		phi = 0.0f;
		psi = (atan2f(dcm[1][2] - dcm[0][1],
		              dcm[0][2] + dcm[1][1]) + phi);

	} else if(fabsf(theta + (float)M_PI_2) < 1.0e-3f) {
		phi = 0.0f;
		psi = atan2f(dcm[1][2] - dcm[0][1],
		             dcm[0][2] + dcm[1][1] - phi);

	} else {
		phi = atan2f(dcm[2][1], dcm[2][2]);
		psi = atan2f(dcm[1][0], dcm[0][0]);
	}

	*roll = phi;
	*pitch = theta;
	*yaw = psi;
}


/**
 * Converts a quaternion to euler angles
 *
 * @param quaternion a [w, x, y, z] ordered quaternion (null-rotation being 1 0 0 0)
 * @param roll the roll angle in radians
 * @param pitch the pitch angle in radians
 * @param yaw the yaw angle in radians
 */
MAVLINK_HELPER void mavlink_quaternion_to_euler(const float quaternion[4], float* roll, float* pitch, float* yaw)
{
	float dcm[3][3];
	mavlink_quaternion_to_dcm(quaternion, dcm);
	mavlink_dcm_to_euler((const float(*)[3])dcm, roll, pitch, yaw);
}


/**
 * Converts euler angles to a quaternion
 *
 * @param roll the roll angle in radians
 * @param pitch the pitch angle in radians
 * @param yaw the yaw angle in radians
 * @param quaternion a [w, x, y, z] ordered quaternion (null-rotation being 1 0 0 0)
 */
MAVLINK_HELPER void mavlink_euler_to_quaternion(float roll, float pitch, float yaw, float quaternion[4])
{
	float cosPhi_2 = cosf(roll / 2);
	float sinPhi_2 = sinf(roll / 2);
	float cosTheta_2 = cosf(pitch / 2);
	float sinTheta_2 = sinf(pitch / 2);
	float cosPsi_2 = cosf(yaw / 2);
	float sinPsi_2 = sinf(yaw / 2);
	quaternion[0] = (cosPhi_2 * cosTheta_2 * cosPsi_2 +
	                 sinPhi_2 * sinTheta_2 * sinPsi_2);
	quaternion[1] = (sinPhi_2 * cosTheta_2 * cosPsi_2 -
	                 cosPhi_2 * sinTheta_2 * sinPsi_2);
	quaternion[2] = (cosPhi_2 * sinTheta_2 * cosPsi_2 +
	                 sinPhi_2 * cosTheta_2 * sinPsi_2);
	quaternion[3] = (cosPhi_2 * cosTheta_2 * sinPsi_2 -
	                 sinPhi_2 * sinTheta_2 * cosPsi_2);
}


/**
 * Converts a rotation matrix to a quaternion
 * Reference:
 *  - Shoemake, Quaternions,
 *  http://www.cs.ucr.edu/~vbz/resources/quatut.pdf
 *
 * @param dcm a 3x3 rotation matrix
 * @param quaternion a [w, x, y, z] ordered quaternion (null-rotation being 1 0 0 0)
 */
MAVLINK_HELPER void mavlink_dcm_to_quaternion(const float dcm[3][3], float quaternion[4])
{
	float tr = dcm[0][0] + dcm[1][1] + dcm[2][2];

	if(tr > 0.0f) {
		float s = sqrtf(tr + 1.0f);
		quaternion[0] = s * 0.5f;
		s = 0.5f / s;
		quaternion[1] = (dcm[2][1] - dcm[1][2]) * s;
		quaternion[2] = (dcm[0][2] - dcm[2][0]) * s;
		quaternion[3] = (dcm[1][0] - dcm[0][1]) * s;
	} else {
		/* Find maximum diagonal element in dcm
		 * store index in dcm_i */
		int dcm_i = 0;
		int i;

		for(i = 1; i < 3; i++) {
			if(dcm[i][i] > dcm[dcm_i][dcm_i]) {
				dcm_i = i;
			}
		}

		int dcm_j = (dcm_i + 1) % 3;
		int dcm_k = (dcm_i + 2) % 3;

		float s = sqrtf((dcm[dcm_i][dcm_i] - dcm[dcm_j][dcm_j] -
		                 dcm[dcm_k][dcm_k]) + 1.0f);
		quaternion[dcm_i + 1] = s * 0.5f;
		s = 0.5f / s;
		quaternion[dcm_j + 1] = (dcm[dcm_i][dcm_j] + dcm[dcm_j][dcm_i]) * s;
		quaternion[dcm_k + 1] = (dcm[dcm_k][dcm_i] + dcm[dcm_i][dcm_k]) * s;
		quaternion[0] = (dcm[dcm_k][dcm_j] - dcm[dcm_j][dcm_k]) * s;
	}
}


/**
 * Converts euler angles to a rotation matrix
 *
 * @param roll the roll angle in radians
 * @param pitch the pitch angle in radians
 * @param yaw the yaw angle in radians
 * @param dcm a 3x3 rotation matrix
 */
MAVLINK_HELPER void mavlink_euler_to_dcm(float roll, float pitch, float yaw, float dcm[3][3])
{
	float cosPhi = cosf(roll);
	float sinPhi = sinf(roll);
	float cosThe = cosf(pitch);
	float sinThe = sinf(pitch);
	float cosPsi = cosf(yaw);
	float sinPsi = sinf(yaw);

	dcm[0][0] = cosThe * cosPsi;
	dcm[0][1] = -cosPhi * sinPsi + sinPhi * sinThe * cosPsi;
	dcm[0][2] = sinPhi * sinPsi + cosPhi * sinThe * cosPsi;

	dcm[1][0] = cosThe * sinPsi;
	dcm[1][1] = cosPhi * cosPsi + sinPhi * sinThe * sinPsi;
	dcm[1][2] = -sinPhi * cosPsi + cosPhi * sinThe * sinPsi;

	dcm[2][0] = -sinThe;
	dcm[2][1] = sinPhi * cosThe;
	dcm[2][2] = cosPhi * cosThe;
}

#endif
